It is often required in the event of a building fire to ventilate the roof to allow for proper, predictable airflow through the structure. This is done at times with an axe. However the advent of lightweight, high powered chainsaws has led to roof ventilation using such saws. While the use of chainsaws for ventilation purposes simplifies and adds a degree of safety to the process, added hazards have become evident.
Chainsaw cutting chains travel at a high linear velocity and if the blade catches on a hard surface such as a nail, there is a natural tendency for the saw to kick back forcefully toward the user. Also the blade is a constant hazard when operating if left exposed.
Another problem realized is that the powerful saws will usually easily cut to a depth equal to the length of the cutting bar. This is far too great a distance, especially in most situations where it is not desired to cut through the roof rafters. It is far more typical that only the roof covering must be removed and that the rafters be left uncut in order to maintain the structural integrity of the building roof.
A need has thus become felt for a device mountable to a chainsaw that will cover the blade and thereby add a degree of operational safety, and for such device to also have the ability to set the effective depth of cut.
This need has been realized to a degree, and as a result, depth setting bar gauges have been produced. Such gauges are usually somewhat integrated with the chainsaw and are adjustable to set a working depth of cut. The nature of such gauges is that the depth, once set, remains a permanent adjustment until the gauge is intentionally reset at a different cutting depth. This means the blade tip is exposed until the adjustment is manually readjusted to a "zero" cutting depth where the blade is once again covered by the gauge. The kickback hazard and danger from the exposed blade length thus remains until the user manually resets the gauge back to the "zero" cutting depth setting.
A need thus remains for a cutting depth gauge that will function to automatically return to a "zero" depth setting when the saw is cutting to the selected depth, and that will automatically set itself to any depth short of a selected maximum cutting depth during such use.
With such a gauge, as is described and claimed below, safety is maximized even in the event of a kickback. Should the blade encounter a hard object and forcibly kick back toward the user, the automatic function of the depth gauge to "zero out" will protect the user from injury.
It is also desirable for such a gauge that can be selectively changed from the above described automatic mode to a manually secured cutting depth and that can subsequently be easily and quickly returned to a "zero" cutting depth setting.